Metallic gloss finish has been widely employed on steel products and other metal goods (e.g. automobile bodies). The finish is generally formed by coating socalled "metallic" paint which contains granulated metal pigment, such as aluminum powder or flakes.
Hitherto, the metallic paint has been generally organic solvent borne, but it is cautioned nowadays that organic solvent is associated with environment pollutions. It is therefore proposed to replace the organic solvent for water. However, the use of water in turn provides a problem that water is reacted with metallic pigment to produce hydrogen gas which is dangerous. This problem is more serious in automobile industry in which paint is stored in a closed container for a relatively long period of time before use.
In order to overcome the problem associated with the metallic pigment, especially aluminum pigment, many approaches are proposed. For example, Japanese Kokai Publication 58-168670 discloses that the aluminum pigment is treated with phosphoric esters and formulated into an aqueous coating composition. The coating composition, when coated on the substrate, has poor water resistance and poor peeling resistance.
Japanese Kokai Publication 61-47771 based on UK Ser. No. 849719 discloses an aqueous metallic coating composition which contains a reaction product of orthophosphoric acid and an epoxy compound. Also, Japanese Kokai Publication 1-190765 based on U.S. Ser. No. 130,922 discloses an aqueous metallic coating composition which contains an acryl polymer modified with orthophosphoric acid. The both coating compositions still are poor in adhesive properties with a substrate.
DE-OS 3,020,073 discloses that metallic pigment is mixed with a phosphoric ester of a long chain alcohol to form a pigment paste composition which is dispersible in water. In this technique, the phosphoric ester is strongly adhered on the surface of the metallic pigment which, therefore, does not contact with an aqueous medium, thus no hydrogen gas being produced. EP-AI-0133644 proposes a stabilizing technique of metallic pigment, using a compound prepared by neutralizing a phosphoric ester of alkyl phenols with an amine. This compound also has the same function as the phosphoric ester of DE-OS 3,020,073. However, the compounds used in these two patents have hydrophobic segments and require large amounts of an emulsifier to sufficiently disperse the pigment in an aqueous medium. If the emulsifier is not used in such large amounts, the pigment particles agglomerate and therefore provide poor surface appearance. The large amounts of the emulsifier adversely affect on water resistance and adhesive properties with the substrate.